Intelligence reveals North Vietnamese units in South Vietnam - Apr 21, 1965 - HISTORY.com

The Central Intelligence Agency and the Defense Intelligence Agency report a “most ominous” development: a regiment of the People’s Army of Vietnam–the regular army of North Vietnam–division is now operating with the Viet Cong in South Vietnam.

Prior to this, it was believed that South Vietnam was dealing with an internal insurgency by the Viet Cong; the report detailed that, in fact, the Viet Cong forces were being joined in the war against the Saigon government by North Vietnamese army units. In short, the report revealed that South Vietnam was now involved in a much larger war than originally believed. The situation far outstripped the combat capability of the South Vietnamese forces. In order to stabilize the situation, President Lyndon B. Johnson would have to commit U.S. ground combat units, leading to a much greater American involvement in the war. Indeed, eventually over 500,000 U.S. troops were stationed in South Vietnam.